1. Field of the Invention
The present invention relates to a keyboard designed to be used with a small handheld personal information device.
2. Discussion of the Related Art
Integrated circuits have enabled the proliferation of handheld miniature computers with powerful storage, processing, and communication capabilities. These computers include what are known as "personal digital assistants", which are used for such applications as information organization, "personal communicators", or other information access applications. Collectively, such devices are popularly known as personal information devices (PIDs). As PIDs continue to be miniaturized for portability reasons, equipping these PIDs with "QWERTY" style keyboards as primary input devices has become impractical. Any attempt to implement a full keyboard on a PID inevitably results in a design with either keys that are arranged too close for comfortable and accurate operation, or a PID housing which is significant larger than desired, or both. For example, many electronic organizers with a full computer keyboard are simply too big to be carried like a pager (e.g. clipped to a belt, or comfortably placed in a shirt pocket.
To provide a small and convenient character input mechanism, two classes of methods have been tried. The first class of methods attempts to eliminate the keyboard altogether, and the second class of methods attempts to encode additional characters on each of a limited number of keys, by adding modifier keys such as control, alternate, special function etc.
The first class of methods includes handwriting and voice recognition techniques. However, handwriting recognition not only requires a powerful processor in the PID, it has proved to be quite unreliable. Voice recognition, an even more computationally intensive technique, has also been tried. Like handwriting recognition, voice recognition is error-prone, even after the user has invested a significant amount of time in training the device. Voice input is also impractical because of lack of privacy and is socially unacceptable in many occasions.
Yet another alternative provides "soft keys". Under the soft key approach, a touch-sensitive screen displays an image of a keyboard and the user is provided a pen or stylus to select the keys from the keyboard image on the screen. At least three problems are associated with the soft key approach. First, data entry in a soft key keyboard is slow because only one character can be selected at a time. Further, tactile feedback and spatial memory, which enable high speed data entry on the QWERTY type keyboard, is not available on a soft key keyboard. Second, the stylus is often misplaced. Third, a touch-sensitive screen increases costs and reduces the reliability of the device.
In addition, it is desired to minimize both power consumption and the physical size of the PID. Power consumption is minimized if the character input operation does not depend on a computationally intensive mechanism, like the voice or handwriting recognition techniques discussed above. By avoiding computationally intensive operations, a longer battery life between charging results.